In recent years, solar power generation, which does not require fuel or emit greenhouse effect gas, is drawing attention. As for known thin-film solar cell modules used for solar power generation, there are, for example, a thin-film silicon such as amorphous silicon or microcrystal silicon or a thin-film compound such as a thin-film CIS based compound.
For example, a CIS based thin-film solar cell module includes a substrate on which a rear surface electrode layer, a light absorbing layer, and a transparent conductive film are sequentially layered to serve as power generation elements. These layers are divided into multiple cells by multiple division grooves and are configured to be serially connected to each other. For example, a mechanical scribing method that uses a needle and a laser scribing method that uses a laser are known to be methods for forming the division grooves by removing the light absorbing layer on the rear surface electrode layer (see, for example, Patent Document 1).
Further, in order to improve the efficiency of the CIS based thin-film solar cell module, there is a known technique of adding an alkali metal such as sodium (Na) to the light absorbing layer during the forming of the light absorbing layer. A portion of the alkali metal (e.g., sodium (Na)) added to the light absorbing layer spreads throughout the rear surface electrode layer and remains in the rear surface electrode layer. In other words, the rear surface electrode layer is formed to include an alkali metal such as sodium (Na) (see, for example, Patent Document 2).